I saw Muddy Waters in concert in a small college town in Minnesota (Northfield) in the early 70's, and although I was thrilled to see him, I was disappointed in the concert length. First his backup band came on and played a fairly lenghthy set without him. (From seeing other Chicago blues guys, I guess this was a common technique for showing what the band could do without the big guy, and building up suspense). Anyway, then Muddy came on and did a short set, broke a string during the last song (probably Mojo Working), and repeatedly mentioned his broken string as the reason he had to quit.
I felt at the time he could easily have broken the string on purpose, and that he was sort of dissing us as being too small potatoes to lay out any energy (there was a crowded house, but it was a small armory he was playing in). It's also possible he was too sick/tired, or strung out to play (not to mention nearing his final swansong).
Northfield was a great place for some good music then--I saw David Bromberg, Bonnie Raitt, Leo Kottke, Furry Lewis, and Larry Coryell there as well for cheap or free.
Just posting this to see if others had a similar experience...